"I wish that it was obvious when girls got turned on, because they wouldn't be able to talk when they get horny!"
There was a flash, and then nothing. I looked around, and everything seemed the same. Of course, why would it be any different?
I stopped for a moment to think. The wish would be pretty good revenge, but it wasn't perfect. I needed to make sure that the cheerleaders would be affected quickly and often.
"I wish that girls got aroused even more easily than guys." Another flash. That should do the trick.